1. Field of the Invention
The present invention relates to an automatic film-rewinding camera, and more particularly to a method governing automatic rewinding of film in a camera in which a battery-powered motor is used to automatically advance and rewind the film in the camera.
2. Description of the Prior Art
Reference initially will be made to FIG. 1, which shows a camera capable of automatically winding and rewinding the film loaded in the camera. FIG. 1 shows a cross-sectional view of a camera body 1 loaded with a perforated film F contained in a film cartridge P. One end of film F is affixed to a cartridge spool 5. Film F is taken up around a take-up spool 4 in such a manner that the perforations of the film are engaged with a sprocket 3 after passing through a film exposure opening 2. The driving force of a motor (not shown) powered by a battery (not shown) is transmitted to take-up spool 4 or to take-up spool 4 and sprocket 3 so as to wind up film F. Each of the frames on the film thus is displaced as sprocket 3 rotates.
At the moment when the shutter of a camera is released, a frame of film positioned behind the shutter is exposed to light. When the exposure is completed, a start signal for advancing the film is generated by the control circuit and transmitted to a timer. At the same time, the control circuit sends a motor driving signal to the motor to advance the film for just one frame. After the film moves one frame, the shutter is ready to be released for the next exposure. This method of automatically advancing the film is repeated in an automatic film winding camera after each frame is exposed.
In the case of 135 millimeter films available on the market, a perforated film of the length for 12 frames, 24 frames or 36 frames is rolled in a cartridge. In a camera loaded with a cartridge containing a rolled 24 frame film, for example, there is an insufficient length of film beyond the 24th frame to permit the film to be advanced upon exposure of the 24th frame. Thus, the film becomes tensed up as the motor attempts to advance the film to the next frame when the shutter is released. Moreover, since winding the film becomes impossible, the motor becomes overloaded and receives an excess current.
In the conventional method for operating automatic film-rewinding cameras, the film rewind mechanism is controlled in such a manner that, when an excess current flowing into the rewind motor is detected, the motor is stopped, the connection between the motor and take-up spool 4 is interrupted, and cartridge spool 5 is then rotated in reverse.
Conventional methods for controlling automatic film rewinding, which depend on the detection of an abnormality in the film winding operation by detecting an excess current flowing into the winding motor, have several problems. For example, there have been many instances in which, immediately after detecting an abnormality such as a heavy load placed on the film winding mechanism for some reason other than reaching the end of the roll of film, the film is automatically rewound from that point. However, that point might be only halfway to the 24th frame and thus the rest of the film would remain unphotographed.